This invention relates to the regeneration of cationic exchange columns that have been exposed to the chlorate ion. In particular, it relates to the use of sulfite ion during the regeneration of the resin with acid to prevent the formation of chlorine and chlorine dioxide.
Cationic exchange columns can be used to remove undesirable cations, such as calcium and magnesium ions, from liquors that contain chlorate ions. For example, in the electrolysis of sodium chloride, a sodium chloride brine containing small amounts of chlorate can be passed through an ion exchange column to remove calcium and magnesium. Also, in the electrolysis of brine to form chlorate, the recycled sodium chlorate solution, which may contain more than 30% chlorate, can be passed through an ion exchange column to prevent the buildup of calcium and magnesium.
After the cation exchange resin has become exhausted, the resin is regenerated by rinsing with water, replacing the calcium and magnesium on the resin with hydrogen by passing acid through the resin, and, if the sodium form is desired, replacing the hydrogen with sodium by passing a solution of sodium hydroxide through the resin.
However, occasionally the resin will not be thoroughly rinsed and some chlorate will remain on it. Even with several thorough water rinses it is difficult to remove all of the chlorate from the column. If chlorate remains on the column the acid used to condition the column can react with the chlorate remaining on the column to form chlorine gas and chlorine dioxide gas. Chlorine gas can react with the ion exchange resin to degrade it, resulting in a loss of resin capacity. Chlorine dioxide is considered to be a highly dangerous gas because it can explode spontaneously. Until now, no one has found a good way to prevent the formation of chlorine and chlorine dioxide during the regeneration of cationic exchange columns that have been exposed to chlorate.